Prehnitene manufacture by disproportionation



United States Patent PREHNITENE MANUFACTURE BY DISPROPORTIONATION Application December 17, 1956 Serial No. 628,497

3 Claims. (Cl. 260-671) No Drawing.

This invention relates to the disproportionation of pseudocumene. Particularly this invention relates to an accelerated pseudocumene disproportionation process. More particularly the invention relates to the manufacture of prehnitene.

The various tetramethylbenzenes are 'now of commercial interest as starting materials for the production of methylbenzene carboxylic acids and also benzene tetracarboxylic acid. The tetramethylbenzenes can be prepared by the disproportionation of the various trimethylbenzenes. A disability to the disproportionation of trimethylbenzenes lies in the elevated temperatures needed or the prolonged times at lower temperatures.

Prehnitene (1,2,3,4-tetramethylbenzene) occurs in the natural equilibrium mixture of tetramethylbenzenes in amounts on the order of 5 mole percent. The presence of four methyl groups immediately adjacent each other is of considerable interest to chemical manufacturers. Exploitation of this material has been prevented by the very small amount of material available from natural sources, coupled with the cost of handling 9 or 10 volumes of undesired material for each volume of product prehnitene.

An object of the invention is the disproportionation of pseudocumene to tetramethylbenzenes. A particular object is a process for the disproportionation of pseudocumene at a greater rate than obtainable with prior art processes. Another object is the manufacture of prehnitene. A further particular object is the disproportionation of pseudocumene to produce a mixture of tetramethylbenzenes containing considerably more prehnitene than the equilibrium amount. Other objects will become apparent in the course of the detailed description.

The aromatic hydrocarbon feed to the process consists essentially of pseudocumene (1,2,4-trimethylbenzene) and secondary butyl-pseudocumene. It is extremely. dif: ficult to obtain pure pseudocumene. Very high purity material contains on the order of 5% of the other .tri-

V cumene of between about 1:1 and 4:1.

the liquid feed contains between about 20 mole percent methylbenzene isomers and ethyltoluenes. Pseudocumene containing on the order of 5 mole percent of these other C hydrocarbons is suitable for the process. While it is preferred to use a feed containing no non-aromatic hydrocarbons because of the side reactions which occur at the temperatures used with this catalyst pseudocumene containing the two or three percent of paraflinic hydrocarbons present in pseudocumene derived from petroleum sources is suitable for use in the process.

The other component of the liquid feed to the process is secondary butyl-pseudocumene. The secondary butylpseudocumene may be introduced into the reaction zone or premixed with the pseudocumene component, as such. Or the secondary butyl-pseudocurnene may be prepared by alkylating pseudocumene with a normal butene i. e., butene-1 or butene-2. Only enough n-butene is charged to produce the desired liquid feed, i. e., mole ratio of pseudocumene to secondary butyl-pseudocumene of between about 1: 1 and 4: 1. The alkylation reaction may be carried out using any suitable alkylatiou catalyst. It is 2 preferred to use as the alkylation catalyst substantially anhydrous hydrogen fluoride. By the use of the hydrogen fluoride catalyst it is possible to prepare the-liquid feed in situ or transfer the mixture of liquid feed and catalyst to the disproportionation reaction zone without incurring a catalyst separation step.

It is to be noted that approximately the same reaction rate acceleration is obtainable by the use of isopropyl' pseudocumene as the second component of the charge to the reaction zone. Isopropyl xylene which is a biproduct of the disproportionation reaction boils in the same range as the product tetramethylbenzenes and therefore a product recovery problem is introduced by the use of isopropyl pseudocumene. For this reason the instant process is limited to the use of secondary butyl-pseudocumene as the reaction accelerator.

The liquid feed to the process consisting essentially of pseudocumene and secondary butyl-pseudocumene is charged to the reaction zone or contacting zone in a mole ratio of pseudocumene to secondary butylpseudo= In other words and 50 mole percent of the secondary butyl-pseudocumene. In general when maximum disproportionation reaction rate, increase is desired the liquid feed should contain about equal amounts of pseudocumene and secondary butyl-pseudocumene.

The catalyst utilized in the process is liquid hydrogen fluoride. The reaction is carried out under substantially anhydrous conditions; water in the system collects in the catalyst. In general the catalyst should not contain more than about 45% of water. It is preferred to operate under essentially anhydrous conditions with a catalyst containing on the order of 0.5% water. Commercial grade anhydrous hydrofluoric acid is suitable for use in the process. 7

The reaction is a liquid phase one and sufi'icient pressure is maintained on the system to keep the feed and the HF catalyst in the liquid state.

The amount of liquid HF used in the process is between about 25 volume percent and about 400 volume percent calculated with respect to the liquid feed charged to the contacting zone. In general, the liquid HF usage is between about 50 and 200 volume percent. Use of the larger amounts of catalyst has some beneficial effect on the disproportionation reaction rate. One hundred volume percent has been found to be an eminently suitable amount of liquid HF catalyst.

The disproportionation reaction rate is determined by a combination of temperature and time. The lower the temperature the longer the time needed to attain a particular degree of disproportionation. In the accelerated reaction rate process herein described two simultaneous reactions occur. Primarily there is the disproportionation of pseudocumene to produce tetramethylbenzenes. It appears that the tetramethylbenzenes produced from the pseudocumene are mostly durene and prehnitene; these then .isomerize to produce isodurene. It is possible by controlling the time and temperature to produce a tetramethylbenzene product mixture which contains considerably more prehnitene than the equilibrium mixture; in fact the product mixture may contain 3 or more times the theoretical equilibrium of about 5 mole percent of prehnitene.

When it is desired to maximize the tetramethylbenzene product mixture yield the contacting is carried out at'a temperature between about 40 C. and about C.; at these temperatures the contacting is maintained for a time of about 15 minutes and about 300 minutes, the longer times corresponding to the lower temperatures. Thus at about 125 C. the contacting would be maintained for about 15 minutes. In general, it has been found that sufficiently good yields are obtainable by operations at term ture between about 40 C. .and about60 C. The contact-.

ing is maintained for maximum times at each particular temperature. At, about 40 C. the maximumgtime, is about 60 minutes and at about 60 C. the maximum time is about minutes, i. e., the longer-maximum times correspon to h ower emp r r v It a -be n found ha a abou 50 C-it s possible to operate tor a. tim f b ut 60 m nu e t ou bs ant a a ver e efi t on he. pre i ene c nten of th te em hv b p uct V The em y benzen s ane readily sepa a d nt their individual components by a combination of distilet n n fr ion l y l t n- P e ni en may be e ra e by ei h s i on e f ti n on D e s a ily s para d by er et le en- Th bo in p i nd e n 'p n s of h tremethyl nz ne r t out below:

B. P., F. P., 0. C.

196. 9 79.1 I 198. 2 -23. 8 Prehnitene. 205. 1 6. 3

The-results obtainable with the process of the instant invention are illustrated by working examples set out below. It is to be understood that these examples do not limit the invention.

In the runs the secondary butyl-pseudocumene was obtained by introducing butene-l in the desired amount into the reactor after the. pseudocumene had been introduced. In all cases the alkylation reaction was carried out at and 110 C. At these temperatures.

. 4 I at the particular temperature contents were into a polyethylenefiask containing cold water; the whole being contained in a Dry Ice acetone bath. An upper layer of hydrocarbons was separated by decantation from a lower aqueous layer. The hydrocarbons were neutralized before being fractionated into close boiling fractions. The close boiling fractions were analyzed by infrared techniquesto determine the compounds and isomers present. The results of the runs are set out in Table I.

Runs 5 and temperature of 5 these two runs no disproportionation product was produced in spite of the extreme time of contacting.

Runs 1 and 2 were carried out at 98 60 minutes. Run. No. 1 was carried out with pseudocumene alone. In run No. 1 the hydrocarbon product mixture contained 13% of tetramethylbenzenes. The tetramethylbenzenes were very close to theequilibrium concentration. Run No. 2 was carried out with approxi: mately equal amounts of 'pseudocumene and secondary utyl-p eudee m n T e r t o product mixtur ee tained more than twice the amount of tetramethylbenzene than was produced in run No. l. The composition "of the tetramethylbenzene product was the same in No.

2 as in run No. 1.

Runs 3 and 4 were carried out at 50 C. and 60 minutes time. Run No. 3 was with pseudocumene alone and pro; duced a product mixture containing 9% of tetramethyl;

benzenes. The tetramethylbenzene product contained the same distribution of isomers as did the material from run No. 1 at the higher temperature. Run No. 1 70- duced more than double the amountof tetramethylben- Zene produced in run No. 3. In addition to this higher tetramethylbenzene product produced the composition of, the tetramethylbenzene product is very markedly differ? ent than that of run 3. Whereas in run the tetrarnethylbenzene the tetramethylbenz ene product was prehnitene. Thus it is possible to obtain simultaneously an'increased yield of.

TABLE I HF.'I00 vol. percent on feed Run N o 1 2 3 I 4 5 6 Charge, Moles:

' Pseudocumena. 2. 0 2.03 2. 17 2. 17 2. 17 2. 17

Butene-l, moles. 0 1. 01 0 1;. 0 1. 0 0 HF, mo1es 25 25 25 7 I 25 25 25,

Alkylation Temp, C 3 3 3 Reaction Temp C 98 98 50 50 5v 5 Reaction Time, Min 60 60 60 60 1, 080 1, 080 Product Distribution, Mole Percent:

Xyle 13 10 s 5 0 0 Trimethylhenzene- 74 36 83 47 52 100 Tetramethylbenze 13 28 9 20 0 I 0 Sec-Butylxylene I 12 13 0 0' Sec-Butyltrimethylbenzenes and higher 13 15 48 0 Composition of Tetramethylbenzenes, Percent:

urene 45 45 Isodurene.-. 45 v45 '45 25 Prehnitene 10 10 10 25 about Q 0.; theelefin was, introduced at rate such that the temperature was substantially maintained at this low point. After the alkylation was complete the contents of the reacto amely. p e m ne, e ond y y p e doeumen a a y e e b ou t ne the sired disproportignation reaction temperature.

'I'he individual runs were carried out in a 1 liter autoclave provided with a stirrer. The pseudocumene used wasessentially pure material and contained only 1 or 2% f the the r m, flu'l en ne -v Commercial grade ydrous hydrofluoric acid was used as thecatalyst. Essene y Pure bu n -l wee er e t e olefin e h P eduction of secondary butylepseudocumene. I

Fo p pos f com son un w em e t-hem y r ac ion. re eeeel e e P es e m ef e very very markedly in by use of the process of tetramethylbenzene and also creased amounts of prehnitene the instant invention.

Thus having described the invention what is claimed is z 1. A process for the manufacture of prehnitene which process comprises contacting, under substantially anhydrous conditions, a liquid feed consisting essentially of pseudocumene and secondary butyl-pseudocumene, in 1 3. mole ratio of pseudocumene to secondary butyl-pseudo cumene of between about 1:1 and 4: 1, in the presenceof liquid hydrogen fluoride, in an amount of between about 25 and 400 volume percent, based on said feed, ata temperature between about 40 C. and about 60 C. fora maximum time of between about 15 minutes andlabout 60 minutes, the longer maximum times corresponding to the lower temperatures, separating a product hydrocar;

withdrawn 6' were carried out at a disproportionatior C. fora total time of 18 hours. In

C. ata time of l 3 on1y"10%' of i was prehnitene in run 4, 25% of, 1

bon mixture from said HF, separating a product tetraabout 1:1, said temperature is on the order of 50 C. and methylbenzene mixture from said hydrocarbon mixture said time is about 60 minutes. and separating prehnitene from said tetramethylbenzene product mixture, which tetramethylbenzene product mix- References Cited in the file of this Patent ture is characterized by a prehnitene content considerably 5 UNITED STATES PATENTS greater than 10 mole E 2,803,681 McCaulay Aug. 20, 1957 2. The process of dam 1 wherem 531d feed 1s obtained 2,814,651 Mccaulay 25 957 by aikylating pseudocumene with n-butene using liquid HF catalyst and charging the alkylation product and cata- OTHER REFERENCES lyst to said contacting step. 10 Nightingale: Chemical Reviews, vol. 25, 1939, pp.

3. The process of claim 1 wherein said mole ratio is 329-376 (pages 341 and 344 only relied on). 

1. A PROCESS FOR THE MANUFACTURE OF PREHNITENE WHICH PROCESS COMPRISES CONTACTING, UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS, A LIQUID FEED CONSISTING ESSENTIALLY OF PSEUDOCUMENE AND SECONDARY BUTYL-PSEUDOCUMENE, IN A MOLE RATIO OF PSEUDOCUMENE TO SECONDARY BUTYL-PSEUDOCUMENE OF BETWEEN ABOUT 1:1 AND 4:1, IN THE PRESENCE OF LIQUID HYDROGEN FLUORIDE, IN AN AMOUNT OF BETWEEN ABOUT 25 AND 400 VOLUME PERCENT, BASED ON SAID FEED, AT A TEMPERATURE BETWEEN ABOUT 40*C. AND ABOUT 60*C. FOR A MAXIMUM TIME OF BETWEEN ABOUT 15 MINUTES AND ABOUT 60 MINUTES, THE LONGER MAXIMUM TIMES CORRESPONDING TO THE LOWER TEMPERATURES, SEPARATING A PRODUCT HYDROCARBON MIXTURE FROM SAID HF, SEPARATING A PRODUCT TETRAMETHYLBENZENE MIXTURE FROM SAID HYDROCARBON MIXTURE AND SEPARATING PREHNITENE FROM SAID TETRAMETHYLBENZENE PRODUCT MIXTURE, WHICH TETRAMETHYLBENZENE PRODUCT MIXTURE IS CHARACTERIZED BY A PREHNITENE CONTENT CONSIDERABLY GREATER THAN 10 MOLE PERCENT. 